1. Field of the Invention
The present invention relates to an error correction method and circuit for nonlinear quantization circuit, and in particular, to the method and circuit that can automatically correct characteristic dispersion of a nonlinear circuit of the nonlinear quantization circuit or deviation from a predetermined nonlinear curve of the nonlinear circuit, which results from deterioration of the nonlinear circuit with age, or from the influence of environmental temperature.
2. Description of the Prior Art
Nonlinear quantization, for example of a video signal, is performed by analog-to-digital conversion of the video signal after it undergoes nonlinear conversion by a nonlinear circuit having a nonlinear characteristic curve as shown in FIG. 1. This enables the quantization circuit to improve the resolution for signals smaller than the middle amplitude of the video signal. The nonlinear curve in FIG. 1 is expressed by the following equation. EQU y=x.sup.n (n&lt;1.0)
One example of the nonlinear conversion circuits is a gamma correction circuit used in a color television camera. The gamma correction circuit nonlinearly converts the video signal by using the nonlinear characteristics of semiconductor devices such as transistors and diodes. Therefore, the conversion characteristics of the gamma correction circuit tend to produce errors resulting from the deterioration with age and the influence of environmental temperature. Since the error occurs independently in each nonlinear circuit of the RGB channels, it causes color tone changes of an image. Therefore, each nonlinear circuit of the RGB channels must be strictly adjusted to have an identical curve.
Thus, the conventional nonlinear quantization circuit requires an analog nonlinear circuit of high stability and tedious adjustment.